Field of the Invention
The present invention relates to flywheels, particularly to concentric, multiple ring rotors or flywheels, and more particularly to a concentric ring flywheel or rotor wherein the adjacent rings are configured to eliminate the need for differential expansion separators between the adjacent rings.
The use of flywheels for the storage of energy has long been known, and the application of flywheels for vehicular use was initialed decades ago. The storage of energy in a flywheel to power an elective vehicle was utilized, for example over forty years ago to operate an electric-drive bus, known as the Gyrobus. In this electric-drive bus, occasional charging stops were required for an electric motor to spin up a heavy steel flywheel, and in motion this flywheel provided energy to power the motor connected to it, which then operated as a generator, to provide electricity to drive other electric motors that turned the wheels of the bus. Using the reversibility of the generator-motor, in slowing down or on downhill runs the bus spun up the flywheel, thereby providing a "regenerative" braking action that at the same time recovered some of the energy expended in driving the bus. The main drawbacks of this Gyrobus were the cumbersome steel flywheel and the cumbersome and expensive power conversion equipment.
The use of flywheels in the form of an electromechanical battery (EMB) was extensively researched in the 1970-1980 time period for use in electric vehicles to reduce the consumption of fuel by internal combustion engines and increase the air quality. It was determined from these efforts that the addition of one or more EMBs to the conventional battery system could greatly improve the performance of the electric vehicles.
With the development of strong, lightweight materials and solid-state electronics, EMBs were again considered for electric vehicle use, as well as for large stationary applications.. Such materials induced fiber composites, with the flywheels, which included contra-rotating rotors each being composed of multiple, concentric rings. For example, compact cylindrical flywheels using unidirectionally wound flexible fibers were developed. U.S. Pat. No. 3,683,216 issued Aug. 8, 1972 to R. F. Post, and No. 3,741,034 issued Jun. 26, 1973 to S. F. Post, exemplify flywheels with multi-ring contrarotating rotors.
Further research and development efforts have been directed to fiber composite flywheels using a multi-ring design. For example, one approach consisted of separate thin-walled cylinders or rings fabricated of filament-wound uni-directional fibers embedded in an epoxy matrix, and the cylinders were coupled together by elastic elements or spring-like mechanical elements that transmit torques but did not transmit strong radial forces. Such an approach, along with an extensive history of flywheel development is set forth in a paper UCRL-JC-110861, "A High Efficiency Electromechanical Battery", by R. F. Post et al, Jun. 11, 1992.
Concentric ring or multi-ring flywheels have unique features that minimize radial tensile stress allowing higher speeds and increased stored energy. However, a difficult aspect of this methodology is that the concentric rings expand differentially with different radius rings. This differential expansion between rings requires the use of expandable separators therebetween to take up the gap formed between adjacent rings. These separators are required to be dynamic components.
While elastic and spring-like elements were utilized to interconnect the cylinders or rings of the flywheel described in the above-referenced paper UCRL-JC-110861, such did not effectively provide for the differential expansion of the various rings, or maintain a torque and centering attachment between the adjacent rings. Recently, an expandable separator/torque coupler between the rings of a concentric ring rotor or flywheel has been developed using an expandable hook ring carbon fiber approach. Such is described and claimed in copending U.S. application Ser. No. 08/316,685, filed Sep. 30, 1994, entitled "Concentric Ring Flywheel With Hooked Ring Carbon Fiber Separator/Torque Coupler", assigned to the same assignee.
While these prior approaches to solve the differential expansion problem of concentric rings rotors or flywheels have been successful, the cost, added weight, etc., associated with expandable separators, is a factor in the overall development of efficient flywheel utilization. Thus, elimination of these additional components while providing a solution to the differential expansion problem associated with concentric ring rotor assemblies, such as flywheel, would be a significant advance in this field of technology. The present invention provides a solution to the differential expansion problem without the use of differential expansion separators. This is accomplished by providing each pair of adjacent concentric rings with matching circumferential steps, whereby spin-up of the concentric rings do not form the gap between rotors produced by differential expansion due to the different radius of the rings, thereby eliminating the need for expansion separators to take up the gap formed by the adjacent concentric rings.